"For the love of Italy, one can do crazy and wise things," Berlusconi said in a statement Wednesday. "Eighteen years ago I came into office, a foolhardy venture not devoid of wisdom. Now I choose to take a step back, for the same love that moved me to act back then."
The 76-year-old media mogul, whose third tenure as premier ended last year with Italy facing economic troubles and him embroiled in sex scandals, including his current trial on charges he had sex with an underage prostitute, said his People of Freedom party would hold primaries to pick a candidate by the end of December, the Italian news agency ANSA reported.
Mario Monti, a political independent, replaced Berlusconi as prime minister in November.
In Milan, Karima El Mahroug, the Moroccan belly dancer known as Ruby, who Berlusconi is accused of paying for sex, said Thursday she is eager to testify on behalf of Berlusconi.
"I'm the lightning rod of this trial and they should call on me," she told Italian television. "I can't wait, and when they do, I'll go."
Prosecutors allege she is one of 33 prostitutes Berlusconi had sex with at so-called bunga bunga parties at his home near Milan.
If convicted, Berlusconi could be sent to jail for up to three years for having sex with an underage prostitute and up to 12 years for abuse of office, ANSA said.